The application of novel biological therapeutics based on molecular medicine knowledge is often complicated by the large size of these compounds. Most biological therapeutics with a pronounced specificity, such as antibodies, possess a high molecular weight, but which results in unfavourable pharmacokinetic qualities setting hurdles for their clinical applications. The successful clinical application of many high molecular weight drugs is hampered by their inability to efficiently bind to their target cell surfaces and/or traverse the cellular membrane (Sarko et al., 2010).
For example, antibodies and immunoglobulin-based agents are widely used in therapies for an increasing number of human malignancies (Waldmann 2003), especially cancer (Oldham & Dillman, 2008). Besides immunotherapeutic regimens based on antibody-dependent cellular cytotoxicity (ADCC) and/or complement-dependent cytotoxicity (CDC), immunoconjugates charged with toxins or radionuclides have been developed to enhance the antitumor potency (Carter 2001). The latter mode of treatment is known as radioimmunotherapy (RAIT), a concept which was proposed in the early 1950s. Now, almost 60 years later, there are only two radiolabeled antibodies, 90Y-ibritumomab tiuxetan (Zevalin®, Spectrum Pharmaceuticals) and 131I-tositumab (Bexxar®, GlaxoSmithKline), approved for clinical use (Witzig et al., 2002; Kaminski et al., 2001). Application of these two is indicated for patients with relapsed or refractory, low grade, follicular or transformed, non-Hodgkin's lymphoma (NHL). NHLs are good targets for RAIT, because they often are highly sensitive to radiation. Solid tumors are usually slow in growth and thus successful treatment remains a challenge. Especially, as full size antibodies have poor pharmacokinetic properties, i.e. slow binding kinetics and poor clearance, which results in collateral radiation-based damage (Song & Sgouros, 2011; Pouget et al., 2011), their usage in radioimmunodetection (RAID) and RAIT of cancer is limited. A plethora of antibody-based fragments and pretargeting approaches have been developed.
Cell-penetrating peptides are a relatively new class of short peptide sequences that cross the cytoplasmic membrane efficiently. Notably, when coupled to a cargo payload, they facilitate cellular uptake of the cargo. They have a broad range of possible applications in drug delivery and molecular biology (Fonseca at al., 2009; Howl et al., 2007; Kersemans et al., 2008). Antibody modifications with single CPPs have been reported in literature but mainly for molecular imaging (Hu et al., 2007; Cornelissen et al., 2007; Hu et al. 2006) and not for tumor therapy or detection. The only example for a successful application of CPPs in radioimmunoscintigraphy, is the modification of a divalent single-chain fragment of the anti-tumor-associated glycoprotein 72 monoclonal antibody CC49. When co-administered with a CPP, the tumor uptake and tumor-to-normal tissue ratio of the fragment increased significantly in tumor xenografts at 24 h (Jain et al., 2005). In contrast to single chain fragments, full-size monoclonal, tumor-targeting antibodies are readily available and clinically tested. Therefore, means and methods to improve their tumor-retention and pharmacokinetic properties are desired.
Small branched synthetic peptide conjugates were developed as vehicles for the delivery of diagnostic probes and cytotoxic agents into the cytoplasm and the nucleus (Sheldon et al., 1995; WO 95/33766 A1), which are particularly suitable as transfection agents (Singh et al., 1999).
Furthermore, means and methods to improve further clinically relevant proteins, such as coagulation factors, that improve their pharmacokinetic properties are desired.
There is a need in the art for providing means and methods for improving the pharmacokinetics and/or internalization of biologically or clinically relevant and/or therapeutic proteins, in particular to improve their use for the diagnosis and treatment of diseases.